The flow and transport phenomena in granular soils are predominantly governed by the intricate internal structure of the pore space, which is fundamentally determined by grain size distribution and their spatial arrangement. The characterization of grain-scale packing structures and reliable prediction of flow properties in granular soils, exhibiting broad particle size distributions continue to pose substantial theoretical and computational challenges. In this study, the numerical procedures of granular soils generation, multiscale pore-network construction and flow property simulation were systematically applied to granular soils with grain size distribution covering multiple orders of magnitude. Various granular soils are well generated through dividing the grain size distribution into various intervals with a size ratio not greater than 10 at different length scales. The corresponding topologically equivalent networks of pores and throats are extracted and combined to construct a single multiscale pore-network, which includes pore elements ranging over four orders of magnitude in size, and makes up for the lack of small pore description through X-ray computed tomography method. The flow characteristics of different granular soils are further simulated through the multiscale pore-network modeling, where water retention curves are in good agreement with experimental data, and the intrinsic permeability as well gas diffusivity is also accurately predicted. The findings of this study provide valuable insights into how grain size distribution influences pore structure and macroscopic flow properties. The developed multiscale pore-network model herein establishes a comprehensive framework that enables comprehensive investigation of more complex mechanisms, including physical-chemical- biological interactions and other flow phenomena at the pore scale.
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